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Saturday, June 30, 2012

In the first side-by-side tests of a half-dozen palladium- and iron-based catalysts for cleaning up the carcinogen TCE, Rice University scientists have found that palladium destroys TCE far faster than iron -- up to a billion times faster in some cases.

The results will appear in a new study in the August issue of the journal Applied Catalysis B: Environmental.

TCE, or trichloroethene, is a widely used chemical degreaser and solvent that's found its way into groundwater supplies the world over. The TCE molecule, which contains two carbon atoms and three chlorine atoms, is very stable. That stability is a boon for industrial users, but it's a bane for environmental engineers.

"It's difficult to break those bonds between chlorine and carbon," said study author Michael Wong, professor of chemical and biomolecular engineering and of chemistry at Rice. "Breaking some of the bonds, instead of breaking all the carbon-chlorine bonds, is a huge problem with some TCE treatment methods. Why? Because you make byproducts that are more dangerous than TCE, like vinyl chloride.

CAPTION: Michael Wong, CREDIT: Rice University

"The popular approaches are, thus, those that do not break these bonds. Instead, people use air-stripping or carbon adsorption to physically remove TCE from contaminated groundwater," Wong said. "These methods are easy to implement but are expensive in the long run. So, reducing water cleanup cost drives interest in new and possibly cheaper methods."

In the U.S., TCE is found at more than half the contaminated waste sites on the Environmental Protection Agency's Superfund National Priorities List. At U.S. military bases alone, the Pentagon has estimated the cost of removing TCE from groundwater to be more than $5 billion.

In the search for new materials that can break down TCE into nontoxic components, researchers have found success with pure iron and pure palladium. In the former case, the metal degrades TCE as it corrodes in water, though sometimes vinyl chloride is formed. In the latter case, the metal acts as a catalyst; it doesn't react with the TCE itself, but it spurs reactions that break apart the troublesome carbon-chlorine bonds.

Because iron is considerably cheaper than palladium and easier to work with, it is already used in the field. Palladium, on the other hand, is still limited to field trials.

Wong led the development of a gold-palladium nanoparticle catalyst approach for TCE remediation in 2005. He found it was difficult to accurately compare the new technology with other iron- and palladium-based remediation schemes because no side-by-side tests had been published.

Caption: This is a scanning electron microscopy image showing a palladium nanoparticle with a gold antenna to enhance plasmonic sensing.

"People knew that iron was slower than palladium and palladium-gold, but no one knew quantitatively how much slower," he said.

In the new study, a team including Wong and lead author Shujing Li, a former Rice visiting scholar from Nankai University, China, ran a series of tests on various formulations of iron and palladium catalysts. The six included two types of iron nanoparticles, two types of palladium nanoparticles -- including Wong's palladium-gold particle -- and powdered forms of iron and palladium-aluminum oxide.

The researchers prepared a solution of water contaminated with TCE and tested each of the six catalysts to see how long they took to break down 90 percent of the TCE in the solution. This took less than 15 minutes for each of the palladium catalysts and more than 25 hours for the two iron nanoparticles. For the iron powder, it took more than 10 days.

"We knew from previous studies that palladium was faster, but I think everyone was a bit surprised to see how much faster in these side-by-side tests," Li said.

Wong said the new results should be helpful to those who are trying to compare the costs of conducting large-scale tests on catalytic remediation of TCE.

Additional co-authors include former Rice undergraduate Chris Romanczuk, former Rice graduate student Yu-Lun Fang and faculty members Zhaohui Jin and Tielong Li, both of Nankai University. The research was supported by the National Science Foundation, the Welch Foundation and the China Scholarship Council.

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Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is known for its "unconventional wisdom." With 3,708 undergraduates and 2,374 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice has been ranked No. 1 for best quality of life multiple times by the Princeton Review and No. 4 for "best value" among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to www.rice.edu/nationalmedia/Rice.pdf.

Saturday, June 23, 2012

Nano-infused paint can detect strain - HOUSTON – A new type of paint made with carbon nanotubes at Rice University can help detect strain in buildings, bridges and airplanes.

The Rice scientists call their mixture “strain paint” and are hopeful it can help detect deformations in structures like airplane wings. Their study, published online this month by the American Chemical Society journal Nano Letters details a composite coating they invented that could be read by a handheld infrared spectrometer.

This method could tell where a material is showing signs of deformation well before the effects become visible to the naked eye, and without touching the structure. The researchers said this provides a big advantage over conventional strain gauges, which must be physically connected to their read-out devices. In addition, the nanotube-based system could measure strain at any location and along any direction.

Rice chemistry professor Bruce Weisman led the discovery and interpretation of near-infrared fluorescence from semiconducting carbon nanotubes in 2002, and he has since developed and used novel optical instrumentation to explore nanotubes’ physical and chemical properties.

An illustration shows how polarized light from a laser and a near-infrared spectrometer could read levels of strain in a material coated with nanotube-infused paint invented at Rice University. (Credit: Bruce Weisman/Rice University)

Satish Nagarajaiah, a Rice professor of civil and environmental engineering and of mechanical engineering and materials science, and his collaborators led the 2004 development of strain sensing for structural integrity monitoring at the macro level using the electrical properties of carbon nanofilms – dense networks/ensembles of nanotubes. Since then he has continued to investigate novel strain sensing methods using various nanomaterials.

But it was a stroke of luck that Weisman and Nagarajaiah attended the same NASA workshop in 2010. There, Weisman gave a talk on nanotube fluorescence. As a flight of fancy, he said, he included an illustration of a hypothetical system that would use lasers to reveal strains in the nano-coated wing of a space shuttle.

“I went up to him afterward and said, ‘Bruce, do you know we can actually try to see if this works?’” recalled Nagarajaiah.

Nanotube fluorescence shows large, predictable wavelength shifts when the tubes are deformed by tension or compression. The paint — and therefore each nanotube, about 50,000 times thinner than a human hair — would suffer the same strain as the surface it’s painted on and give a clear picture of what’s happening underneath.

“For an airplane, technicians typically apply conventional strain gauges at specific locations on the wing and subject it to force vibration testing to see how it behaves,” Nagarajaiah said. “They can only do this on the ground and can only measure part of a wing in specific directions and locations where the strain gauges are wired. But with our non-contact technique, they could aim the laser at any point on the wing and get a strain map along any direction.”

He said strain paint could be designed with multifunctional properties for specific applications. “It can also have other benefits,” Nagarajaiah said. “It can be a protective film that impedes corrosion or could enhance the strength of the underlying material.”

Weisman said the project will require further development of the coating before such a product can go to market. “We’ll need to optimize details of its composition and preparation, and find the best way to apply it to the surfaces that will be monitored,” he said. “These fabrication/engineering issues should be addressed to ensure proper performance, even before we start working on portable read-out instruments.”

“There are also subtleties about how interactions among the nanotubes, the polymeric host and the substrate affect the reproducibility and long-term stability of the spectral shifts. For real-world measurements, these are important considerations,” Weisman said.

But none of those problems seem insurmountable, he said, and construction of a handheld optical strain reader should be relatively straightforward. “There are already quite compact infrared spectrometers that could be battery-operated,” Weisman said. “Miniature lasers and optics are also readily available. So it wouldn’t require the invention of new technologies, just combining components that already exist.

“I’m confident that if there were a market, the readout equipment could be miniaturized and packaged. It’s not science fiction.”

Lead author of the paper is Paul Withey, an associate professor of physics at the University of Houston-Clear Lake, who spent a sabbatical in Weisman’s lab at Rice studying the fluorescence of nanotubes in polymers. Co-authors are Rice civil engineering graduate student Venkata Srivishnu Vemuru in Nagarajaiah’s group and Sergei Bachilo, a research scientist in Weisman’s group.

Support for the research came from the National Science Foundation, the Welch Foundation, the Air Force Research Laboratory and the Infrastructure-Center for Advanced Materials at Rice.

Dublin, June 11th, 2012 − New groundbreaking research by scientists at Trinity College Dublin has found that exposure to nanoparticles can have a serious impact on health, linking it to rheumatoid arthritis and the development of other serious autoimmune diseases. The findings that have been recently published in the international journal 'Nanomedicine' have health and safety implications for the manufacture, use and ultimate disposal of nanotechnology products and materials. They also identified new cellular targets for the development of potential drug therapies in combating the development of autoimmune diseases.

Environmental pollution including carbon particles emitted by car exhaust, smoking and long term inhalation of dust of various origins have been recognised as risk factors causing chronic inflammation of the lungs. The link between smoking and autoimmune diseases such as rheumatoid arthritis has also been established. This new research now raises serious concerns in relation to similar risks caused by nanotechnology products which if not handled appropriately may contribute to the generation of new types of airborne pollutants causing risks to global health.

Yuri Volkov received his MD from the Moscow Medical Academy and subsequently a PhD in biomedical sciences at the Institute of Immunology, Moscow. He has been working at the Department of Clinical Medicine, Trinity College Dublin since 1995 and is currently also one of the Principal Investigators at the Institute of Molecular Medicine. PHOTO CREDIT: Trinity College Dublin

In their research, the Nanomedicine and Molecular Imaging team at Trinity College Dublin's School of Medicine led by Professor of Molecular Medicine, Yuri Volkov investigated whether there was a common underlying mechanism contributing to the development of autoimmune diseases in human cells following their exposure to a wide range of nanoparticles containing different physical and chemical properties.

The scientists applied a wide range of nanomaterials including ultrafine carbon black, carbon nanotubes and silicon dioxide particles of different sizes, ranging from 20 to 400 nanometres, to human cells derived from the lining of the airway passages, and to the cells of so-called phagocytic origin − those cells that are most frequently exposed to the inhaled foreign particles or are tasked with cleaning up our body from them. At the same time, collaborating researchers from the Health Effects Laboratory Division, National Institute for Occupational Safety & Health (Morgantown, WV, USA) have conducted the studies in mice exposed to chronic inhalation of air contaminated with single walled carbon nanotubes.

The result was clear and convincing: all types of nanoparticles in both the TCD and US study were causing an identical response in human cells and in the lungs of mice, manifesting in the specific transformation of the amino acid arginine into the molecule called citrulline which can lead to the development of autoimmune conditions such as rheumatoid arthritis.

In the transformation to citrulline, human proteins which incorporate this modified amino acid as building blocks, can no longer function properly and are subject to destruction and elimination by the bodily defence system. Once programmed to get rid of citrullinated proteins, the immune system can start attacking its own tissues and organs, thereby causing the autoimmune processes which may result in rheumatoid arthritis.

Commenting on the significance of the findings, TCD's Professor Volkov says: "The research establishes a clear link between autoimmune diseases and nanoparticles. Preventing or interfering with the resulting citrullination process looks therefore as a promising target for the development of future preventative and therapeutic approaches in rheumatoid arthritis and possibly other autoimmune conditions."

The paper's full title published in the 'Nanomedicine' journal (Future Medicine journals group) is "Citrullination of proteins: a common post-translational modification pathway induced by different nanoparticles in vitro and in vivo"

Saturday, June 09, 2012

Using synthetic diamond, quantum bit memory can now exceed one second at room temperature, opening up the potential for new solid state quantum based sensors and quantum information processing

7 June 2012: Element Six, the world leader in synthetic diamond supermaterials, working in partnership with academics in Harvard University, California Institute of Technology and Max-Planck-Institut für Quantenoptik, has used its Element Six single crystal synthetic diamond grown by chemical vapour deposition (CVD) to demonstrate the capability of quantum bit memory to exceed one second at room temperature.

This study demonstrated the ability of synthetic diamond to provide the read-out of a quantum bit which had preserved its spin polarisation for several minutes and its memory coherence for over a second. This is the first time that such long memory times have been reported for a material at room temperature, giving synthetic diamond a significant advantage over rival materials and technologies that require complex infrastructure which necessitates, for example, cryogenic cooling.

The versatility, robustness, and potential scalability of this synthetic diamond system may allow for new applications in quantum information science and quantum based sensors used, for example, in nano-scale imaging of chemical/biological processes.

Synthetic diamonds of various colors grown by the high-pressure high-temperature technique

The synthetic diamond technical work was completed by the Element Six synthetic diamond R&D team based at Ascot in the UK who developed novel processes for growing synthetic diamond using chemical vapour deposition (CVD) techniques. Steve Coe, Element Six Group Innovation Director, explained the success of the collaboration:

“The field of synthetic diamond science is moving very quickly and is requiring Element Six to develop synthesis processes with impurity control at the level of parts per trillion – real nano-engineering control of CVD diamond synthesis. We have been working closely with Professor Lukin’s team in Harvard for three years - this result published in Science is an example of how successful this collaboration has been.”

Professor Mikhail Lukin of Harvard University’s Department of Physics described the significance of the research findings:

“Element Six’s unique and engineered synthetic diamond material has been at the heart of these important developments. The demonstration of a single qubit quantum memory with seconds of storage time at room temperature is a very exciting development, which combines the four key requirements of initialisation, memory, control and measurement. These findings might one day lead to novel quantum communication and computation technologies, but in the nearer term may enable a range of novel and disruptive quantum sensor technologies, such as those being targeted to image magnetic fields on the nano-scale for use in imaging chemical and biological processes.”

The findings represent the latest developments in quantum information processing, which involves manipulating individual atomic sized impurities in synthetic diamond and exploiting the quantum property spin of an individual electron, which can be thought of classically as a bar magnet having two states: up (1) and down (0). However, in the quantum mechanical description (physics of the very small), this quantum spin (qubit) can be both 0 and 1 simultaneously. It is this property that provides a framework for quantum computing, but also for more immediate applications such as novel magnetic sensing technologies.

ENDS

Notes to Editors:

About Element Six: Element Six (www.e6.com) is an independently managed synthetic diamond supermaterials company. Element Six is part of the De Beers Family of Companies and is co-owned by Umicore, the Belgian materials group. Element Six is a global leader in the design, development and production of synthetic diamond supermaterials, and operates worldwide with its head office registered in Luxembourg, and primary manufacturing facilities in China, Germany, Ireland, Sweden, South Africa and the UK.

Element Six supermaterial solutions are used in applications such as cutting, grinding, drilling, shearing and polishing, while the extreme properties of synthetic diamond beyond hardness are already opening up new applications in a wide array of industries such as optics, power transmission, water treatment, semi-conductors and sensors.

Funding for some of this research was provided by the DARPA QuASAR programme. The results of the research appear in an article in Science magazine, published 8 June 2012.

Technical details of the research

Key to the material aspect of achieving this result was producing synthetic diamond with essentially no spin impurities other than a very specific defect called the N-V (nitrogen vacancy) centre (a vacancy next to a nitrogen atom in the diamond lattice). This ‘N-V centre’ has very specific properties in that it can be spin polarised (similar to the magnetic difference of North-South or South-North of a bar magnet at room temperature) using a simple green light source. Subsequently, the state of the N-V centre can be read out again using simple techniques within a period limited by the quantum de-coherence time.

The isotope carbon-12 forms 98.9% of the carbon usually found in synthetic diamond, while carbon-13 forms the remaining 1.1%. Carbon 13 has a nuclear spin, which through random thermally driven interactions can interact with the electronic spin of the N-V impurity. Removing as many of these nuclear spins while still maintaining the general high purity of the material was a milestone result for the Element Six CVD R&D team.

Specific to Harvard’s breakthrough was to use a carbon-13 nuclear spin (that was still present) to couple with the N-V electronic spin. While the electron spin has a good de-coherence time, it still fluctuates on the millisecond timescale. Once the electron spin changes its spin, the quantum information (qubit) is lost. A single flip in the electronic spin completely destroys the coherence of the carbon-13 nuclear spin. To prevent the electron flips from affecting the nucleus, the Harvard team reset the electron's spin with green laser light, essentially turning off the interaction between the electron and nucleus when that interaction is not needed. This had the result of creating very fast electron flips which do no interact with the nuclear spin – effectively a non-fluctuating average field.

In combination with this method, the Harvard research team used a sequence of radio-frequency pulses to suppress interactions with other carbon nuclei in the synthetic diamond. As a result, they were able to store quantum information at room temperatures for nearly two seconds, which was significantly more than anticipated when the research commenced. Previous experiments in quantum information have generally demonstrated single qubit memory storage times to be in microseconds.

IMAGE CREDIT: This work has been released into the public domain by its author, NIMSoffice at the wikipedia project. This applies worldwide. In case this is not legally possible: NIMSoffice grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.

HOUSTON — (June 7, 2012) — Thanks to a little serendipity, researchers at Rice University have created a tiny coaxial cable that is about a thousand times smaller than a human hair and has higher capacitance than previously reported microcapacitors.

The nanocable, which is described this week in Nature Communications, was produced with techniques pioneered in the nascent graphene research field and could be used to build next-generation energy-storage systems. It could also find use in wiring up components of lab-on-a-chip processors, but its discovery is owed partly to chance.

“We didn’t expect to create this when we started,” said study co-author Jun Lou, associate professor of mechanical engineering and materials science at Rice. “At the outset, we were just curious to see what would happen electrically and mechanically if we took small copper wires known as interconnects and covered them with a thin layer of carbon.”

CAPTION: An artist’s impression of Rice University’s new coaxial nanocable, which is about a thousand times smaller than a human hair. CREDIT: Zheng Liu/Rice University

The tiny coaxial cable is remarkably similar in makeup to the ones that carry cable television signals into millions of homes and offices. The heart of the cable is a solid copper wire that is surrounded by a thin sheath of insulating copper oxide. A third layer, another conductor, surrounds that. In the case of TV cables, the third layer is copper again, but in the nanocable it is a thin layer of carbon measuring just a few atoms thick. The coax nanocable is about 100 nanometers, or 100 billionths of a meter, wide.

While the coaxial cable is a mainstay of broadband telecommunications, the three-layer, metal-insulator-metal structure can also be used to build energy-storage devices called capacitors. Unlike batteries, which rely on chemical reactions to both store and supply electricity, capacitors use electrical fields. A capacitor contains two electrical conductors, one negative and the other positive, that are separated by thin layer of insulation. Separating the oppositely charged conductors creates an electrical potential, and that potential increases as the separated charges increase and as the distance between them – occupied by the insulating layer — decreases. The proportion between the charge density and the separating distance is known as capacitance, and it’s the standard measure of efficiency of a capacitor.

The study reports that the capacitance of the nanocable is at least 10 times greater than what would be predicted with classical electrostatics.

“The increase is most likely due to quantum effects that arise because of the small size of the cable,” said study co-author Pulickel Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor of Mechanical Engineering and Materials Science.

Lou’s and Ajayan’s laboratories each specialize in fabricating and studying nanoscale materials and nanodevices that exhibit these types of intriguing quantum effects, but Ajayan and Lou said there was an element of chance to the nanocable discovery.

When the project began 18 months ago, Rice postdoctoral researcher Zheng Liu, the lead co-author of the study, intended to make pure copper wires covered with carbon. The techniques for making the wires, which are just a few nanometers wide, are well-established because the wires are often used as “interconnects” in state-of-the-art electronics. Liu used a technique known as chemical vapor deposition (CVD) to cover the wires with a thin coating of carbon. The CVD technique is also used to grow sheets of single-atom-thick carbon called graphene on films of copper.

“When people make graphene, they usually want to study the graphene and they aren’t very interested in the copper,” Lou said. “It’s just used a platform for making the graphene.”

When Liu ran some electronic tests on his first few samples, the results were far from what he expected.

“We eventually found that a thin layer of copper oxide — which is served as a dielectric layer — was forming between the copper and the carbon,” said Liu.

Upon examining other studies more closely, the team found that a few other scientists had made mention of oxidation occurring on the copper substrates during graphene production.

“It’s fairly well-documented, but we couldn’t find anyone who’d done a detailed examination of the electronic properties of such complex interfaces,” Ajayan said.

The capacitance of the new nanocable is up to 143 microfarads per centimeter squared, better than the best previous results from microcapacitors.

Lou said it may be possible to build a large-scale energy-storage device by arranging millions of the tiny nanocables side by side in large arrays.

“The nanoscale cable might also be used as a transmission line for radio frequency signals at the nanoscale,” Liu said. “This could be useful as a fundamental building block in micro- and nano-sized electromechanical systems like lab-on-a-chip devices.”

The research was funded by the National Science Foundation, Rice University, the Office of Naval Research, the Welch Foundation, the Center for Exotic NanoCarbons at Shinshu University and the Japan Regional Innovation Strategy Program by the Excellence.

Co-authors include Lou, Ajayan, Liu, Yongjie Zhan, Gang Shi, Lulu Ma, Wei Gao and Robert Vajtai, all of Rice University; Pradeep Sharma and Mohamed Gharbi of the University of Houston; Simona Moldovan and Florian Banhart, both of Institut de Physique et Chimie des Matériaux in Strasbourg, France; Li Song of Shinshu University in Nagano, Japan; and Jiaqi Huang, formerly of Rice and currently at Tsinghua University in Beijing.

Saturday, June 02, 2012

RICHLAND, Wash. -- Individual homes and entire neighborhoods could be powered with a new, small-scale solid oxide fuel cell system that achieves up to 57 percent efficiency, significantly higher than the 30 to 50 percent efficiencies previously reported for other solid oxide fuel cell systems of its size, according to a study published in this month's issue of Journal of Power Sources.

The smaller system, developed at the Department of Energy's Pacific Northwest National Laboratory, uses methane, the primary component of natural gas, as its fuel. The entire system was streamlined to make it more efficient and scalable by using PNNL-developed microchannel technology in combination with processes called external steam reforming and fuel recycling. PNNL's system includes fuel cell stacks developed earlier with the support of DOE's Solid State Energy Conversion Alliance.

"Solid oxide fuels cells are a promising technology for providing clean, efficient energy. But, until now, most people have focused on larger systems that produce 1 megawatt of power or more and can replace traditional power plants," said Vincent Sprenkle, a co-author on the paper and chief engineer of PNNL's solid oxide fuel cell development program. "However, this research shows that smaller solid oxide fuel cells that generate between 1 and 100 kilowatts of power are a viable option for highly efficient, localized power generation."

Caption: Pacific Northwest National Laboratory developed this highly efficient, small-scale solid oxide fuel cell system that features PNNL-developed microchannel technology and two unusual processes, called external steam reforming and fuel recycling.

Credit: PNNL

Usage Restrictions: Please credit PNNL

Sprenkle and his co-authors had community-sized power generation in mind when they started working on their solid oxide fuel cell, also known as a SOFC. The pilot system they built generates about 2 kW of electricity, or how much power a typical American home consumes. The PNNL team designed its system so it can be scaled up to produce between 100 and 250 kW, which could provide power for about 50 to 100 American homes.

What is an SOFC?

Fuel cells are a lot like batteries in that they use anodes, cathodes and electrolytes to produce electricity. But unlike most batteries, which stop working when they use up their reactive materials, fuel cells can continuously make electricity if they have a constant fuel supply.

SOFCs are one type of fuel cell that operate at higher temperatures - between about 1100 and 1800 degrees Fahrenheit - and can run on a wide variety of fuels, including natural gas, biogas, hydrogen and liquid fuels such as diesel and gasoline that have been reformed and cleaned. Each SOFC is made of ceramic materials, which form three layers: the anode, the cathode and the electrolyte.

Air is pumped up against an outer layer, the cathode. Oxygen from the air becomes a negatively charged ion, O2- , where the cathode and the inner electrolyte layer meet. The ion moves through the electrolyte to reach the final layer, the anode.

There, the oxygen ion reacts with a fuel. This reaction creates electricity, as well as the byproducts steam and carbon dioxide. That electricity can be used to power homes, neighborhoods, cities and more.

The big advantage to fuel cells is that they're more efficient than traditional power generation. For example, the combustion engines of portable generators only convert about 18 percent of the chemical energy in fuel into electricity. In contrast, some SOFCs can achieve up to 60 percent efficiency. Being more efficient means that SOFCs consume less fuel and create less pollution for the amount of electricity produced than traditional power generation, including coal power plants.

Sprenkle and his PNNL colleagues are interested in smaller systems because of the advantages they have over larger ones. Large systems generate more power than can be consumed in their immediate area, so a lot of their electricity has to be sent to other places through transmission lines. Unfortunately, some power is lost in the process. On the other hand, smaller systems are physically smaller in size, so they can be placed closer to power users. This means the electricity they produce doesn't have to be sent as far. This makes smaller systems ideal for what's called distributed generation, or generating electricity in relatively small amounts for local use such as in individual homes or neighborhoods.

Goal: Small and efficient

Knowing the advantages of smaller SOFC systems, the PNNL team wanted to design a small system that could be both more than 50 percent efficient and easily scaled up for distributed generation. To do this, the team first used a process called external steam reforming. In general, steam reforming mixes steam with the fuel, leading the two to react and create intermediate products. The intermediates, carbon monoxide and hydrogen, then react with oxygen at the fuel cell's anode. Just as described before, this reaction generates electricity, as well as the byproducts steam and carbon dioxide.

Steam reforming has been used with fuel cells before, but the approach requires heat that, when directly exposed to the fuel cell, causes uneven temperatures on the ceramic layers that can potentially weaken and break the fuel cell. So the PNNL team opted for external steam reforming, which completes the initial reactions between steam and the fuel outside of the fuel cell.

The external steam reforming process requires a device called a heat exchanger, where a wall made of a conductive material like metal separates two gases. On one side of the wall is the hot exhaust that is expelled as a byproduct of the reaction inside the fuel cell. On the other side is a cooler gas that is heading toward the fuel cell. Heat moves from the hot gas, through the wall and into the cool incoming gas, warming it to the temperatures needed for the reaction to take place inside the fuel cell.

Efficiency with micro technology

The key to the efficiency of this small SOFC system is the use of a PNNL-developed microchannel technology in the system's multiple heat exchangers. Instead of having just one wall that separates the two gases, PNNL's microchannel heat exchangers have multiple walls created by a series of tiny looping channels that are narrower than a paper clip. This increases the surface area, allowing more heat to be transferred and making the system more efficient. PNNL's microchannel heat exchanger was designed so that very little additional pressure is needed to move the gas through the turns and curves of the looping channels.

The second unique aspect of the system is that it recycles. Specifically, the system uses the exhaust, made up of steam and heat byproducts, coming from the anode to maintain the steam reforming process. This recycling means the system doesn't need an electric device that heats water to create steam. Reusing the steam, which is mixed with fuel, also means the system is able to use up some of the leftover fuel it wasn't able to consume when the fuel first moved through the fuel cell.

The combination of external steam reforming and steam recycling with the PNNL-developed microchannel heat exchangers made the team's small SOFC system extremely efficient. Together, these characteristics help the system use as little energy as possible and allows more net electricity to be produced in the end. Lab tests showed the system's net efficiency ranged from 48.2 percent at 2.2 kW to a high of 56.6 percent at 1.7 kW. The team calculates they could raise the system's efficiency to 60 percent with a few more adjustments.

The PNNL team would like to see their research translated into an SOFC power system that's used by individual homeowners or utilities.

"There still are significant efforts required to reduce the overall cost to a point where it is economical for distributed generation applications," Sprenkle explained. "However, this demonstration does provide an excellent blueprint on how to build a system that could increase electricity generation while reducing carbon emissions."